MAINT: Update SliceMode typing

Now a Frequency instance can be used directly as a
valid input for `slice_mode`.

icclim/models/frequency.py

@@ -17,8 +17,6 @@
 
 from icclim.icclim_exceptions import InvalidIcclimArgumentError
 
-SliceMode = Union[str, List[Union[str, Tuple, int]]]
-
 
 def seasons_resampler(
     month_list: list[int],
@@ -232,3 +230,6 @@ def _get_frequency_from_list(slice_mode_list: list) -> Frequency:
             "The sampling frequency must be one of {'season', 'month'}"
         )
     return custom_freq
+
+
+SliceMode = Union[Frequency, str, List[Union[str, Tuple, int]]]

icclim/tests/test_main.py

@@ -8,6 +8,7 @@
 
 import icclim
 from icclim.models.ecad_indices import EcadIndex
+from icclim.models.frequency import Frequency
 from icclim.models.index_group import IndexGroup
 
 
@@ -68,6 +69,18 @@ def test_index_SU(self):
         )
         np.testing.assert_array_equal(0, res.SU)
 
+    def test_index_SU__monthy_sampled(self):
+        res = icclim.index(
+            indice_name="SU",
+            in_files=self.data,
+            out_file=self.OUTPUT_FILE,
+            slice_mode=Frequency.MONTH,
+        )
+        np.testing.assert_array_equal(0, res.SU)
+        np.testing.assert_array_equal(
+            len(np.unique(self.TIME_RANGE.year)) * 12, len(res.time)
+        )
+
     def test_indices_from_DataArray(self):
         res = icclim.indices(
             index_group=IndexGroup.HEAT, in_files=self.data, out_file=self.OUTPUT_FILE